Comfortable diaper

ABSTRACT

An absorbent article, preferably a disposable absorbent article such as a diaper, is disclosed that provides an improved immobilization of absorbent polymer material when the article is fully or partially urine loaded. This absorbent core is useful for providing an absorbent article of increased wearing comfort. Specifically disclosed is an absorbent core useful for an absorbent article comprising a substrate layer and absorbent material, the absorbent material comprising an absorbent polymer material, the absorbent material optionally comprising absorbent fibrous material, the absorbent fibrous material not representing more than 20% of the weight of absorbent polymer material, wherein the absorbent material is immobilized when wet such that the absorbent core achieves a wet immobilization of more than 50%, preferably of more than 60%, 70%, 80% or 90% according to the Wet Immobilization Test described herein.

CROSS REFERENCE TO RELATED APPLICATION

This application is a divisional of U.S. application Ser. No.10/776,851, filed Feb. 11, 2004, the substance of which is incorporatedherein by reference.

FIELD OF THE INVENTION

The present invention concerns an absorbent article, preferably adisposable absorbent article, such as a diaper. The present inventionspecifically concerns an absorbent core for such an absorbent articlethat provides an improved immobilization of absorbent polymer materialwhen the article is fully or partially urine loaded. This absorbent coreis useful for providing an absorbent article of increased wearingcomfort.

BACKGROUND OF THE INVENTION

Absorbent articles, such as diapers and adult incontinence products arewell known articles of staple manufacturing. Multiple attempts have beenmade to provide them with an overall good fit and with a high absorbentcapacity. Modern diapers make use of absorbent polymer materials orso-called superabsorbent materials, which allow for storage of amountsof liquid as high as 300 ml of in a typical baby diaper.

While such a diaper is generally a disposable product it is in someinstances worn over many hours and worn in a dry state as well as in aurine loaded state.

Hence, to provide good wearing comfort it is very important to keep theabsorbent materials of a diaper or other absorbent article in theirintended position, both when the article is dry and when the article isfully or partially loaded with urine (or other bodily liquids).

US Pat. No. 4,381,783 (Elias) discloses an absorbent article with a corecomprising pockets of absorbent hydrocolloid material. These pockets areprovided as to confine the movement of the hydrocolloid material, inparticular when the article is fully or partially loaded with urine. Thepockets form part of an absorbent layer and are typically provided fromcellulose material. Hence, to achieve good immobilization of thehydrocolloid material according to the teaching of this patent, arelatively high amount of cellulosic material is required. Moreover, theprovision of such pockets may hinder the free distribution of liquid tothe more absorbent areas of the core, for example the areas ofhydrocolloid materials.

U.S. Pat. No. 5,944,706 (Palumbo) discloses an absorbent structurecomprising two fibre layers and an intermediate layer. This intermediatelayer comprises an absorbent hydrogel material in an amount exceeding120 g/m² and particles of a thermoplastic material. While thisconstruction certainly provides good immobilisation of the absorbenthydrogel particles in the dry state, it seems that only a lesserimmobilisation can be achieved in the urine loaded state. The disclosedthermoplastic materials appear to swell much less than the disclosedhydrogel materials. Therefore, in particular when the absorbentstructure is to be used in a product to absorb high amounts of liquids,for example a diaper, the wet immobilisation may not be fullysatisfactory.

U.S. Pat. No. 5,411,497 (Tanzer) discloses an absorbent article whichincludes superabsorbent material located in discrete pockets. Theabsorbent article comprises a first and a second carrier layer andwater-sensitive attaching means for securing together the carrier layersand to provide a plurality of pocket regions. The article compriseshigh-absorbency material located within said pocket regions. Thewater-sensitive attachment means provides a wet strength which is lessthan a separating force imparted by a swelling of that high-absorbencymaterial when that high-absorbency material is exposed to an aqueousliquid. The absorbent article is said to provide an absorbent structurewhich more securely locates and contains the high-absorbency material ina selected way of pockets when the article is dry. However, due to theconstruction of the pockets, and specifically due to the selection ofthe water-sensitive attachment means, these pockets are not maintainedwhen the article is fully or partially loaded with liquids. Therefore,it is believed that this absorbent article does not provide a verysatisfactory immobilization of the absorbent material in the fully orpartially urine loaded state.

SUMMARY OF THE INVENTION

The present invention concerns an absorbent article, preferably adisposable absorbent article, such as a diaper. The present inventionspecifically concerns an absorbent core for such an absorbent articlewhich provides an improved immobilization of absorbent polymer materialwhen the article is fully or partially urine loaded. This absorbent coreis useful for providing an absorbent article of increased wearingcomfort. Specifically disclosed is an absorbent core useful for anabsorbent article comprising a substrate layer and absorbent material,the absorbent material comprising an absorbent polymer material, theabsorbent material optionally comprising absorbent fibrous material, theabsorbent fibrous material not representing more than 20% of the weightof absorbent polymer material, wherein the absorbent material isimmobilized when wet such that the absorbent core achieves a wetimmobilization of more than 50%, preferably of more than 60%, 70%, 80%or 90% according to the Wet Immobilization Test described herein.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view of a diaper as a preferred embodiment of anabsorbent article according to the present invention.

FIG. 2 is a cross-sectional view of the diaper shown in FIG. 1 takenalong the sectional line 2-2 of FIG. 1.

FIG. 3 is a cross-sectional view of a preferred embodiment of theabsorbent core.

FIG. 4 is a cross-sectional view of a preferred embodiment of theabsorbent core.

FIG. 5 is a perspective view of a preferred embodiment of the absorbentcore.

FIG. 6 is a cross-sectional view of a preferred embodiment of theabsorbent core.

FIG. 7 is a schematic representation of the rheometer.

FIG. 8 is a schematic view of an apparatus for measuring the Saline FlowConductivity (SFC) value of the hydrogel-forming absorbent polymers.

DETAILED DESCRIPTION OF THE INVENTION

The present invention concerns an absorbent article, preferably adisposable absorbent article, such as a diaper.

As used herein, the following terms have the following meanings:

“Absorbent article” refers to devices that absorb and contain liquid,and more specifically, refers to devices that are placed against or inproximity to the body of the wearer to absorb and contain the variousexudates discharged from the body. Absorbent articles include but arenot limited to diapers, adult incontinence briefs, training pants,diaper holders and liners, sanitary napkins and the like.

“Disposable” is used herein to describe articles that are generally notintended to be laundered or otherwise restored or reused (i.e., they areintended to be discarded after a single use and, preferably, to berecycled, composted or otherwise disposed of in an environmentallycompatible manner).

“Diaper” refers to an absorbent article generally worn by infants andincontinent persons about the lower torso.

“Comprise,” “comprising,” and “comprises” is an open ended term thatspecifies the presence of what follows e.g., a component but does notpreclude the presence of other features, elements, steps or componentsknown in the art, or disclosed herein.

FIG. 1 is a plan view of a diaper 20 as a preferred embodiment of anabsorbent article according to the present invention. The diaper isshown in its flat out, uncontracted state (i.e., without elastic inducedcontraction). Portions of the structure are cut away to more clearlyshow the underlying structure of the diaper 20. The portion of thediaper 20 that contacts a wearer is facing the viewer. The chassis 22 ofthe diaper 20 in FIG. 1 comprises the main body of the diaper 20. Thechassis 22 comprises an outer covering including a liquid pervioustopsheet 24 and/or a liquid impervious backsheet 26. The chassis mayinclude a portion of an absorbent core 28 encased between the topsheet24 and the backsheet 26. The chassis may also include most or all of theabsorbent core 28 encased between the topsheet 24 and the backsheet 26.The chassis preferably further includes side panels 30, elasticized legcuffs 32, and elastic waist feature 34, the leg cuffs 32 and the elasticwaist feature each typically comprise elastic members 33. One endportion of the diaper 20 is configured as a first waist region 36 of thediaper 20. The opposite end portion is configured as a second waistregion 38 of the diaper 20. An intermediate portion of the diaper 20 isconfigured as a crotch region 37, which extends longitudinally betweenthe first and second waist regions 36 and 38. The waist regions 36 and38 may include elastic elements such that they gather about the waist ofthe wearer to provide improved fit and containment (elastic waistfeature 34). The crotch region 37 is that portion of the diaper 20which, when the diaper 20 is worn, is generally positioned between thewearer's legs. The diaper 20 is depicted with its longitudinal axis 10and its transverse axis 12. The periphery of the diaper 20 is defined bythe outer edges of the diaper 20 in which the longitudinal edges 44 rungenerally parallel to the longitudinal axis 100 of the diaper 20 and theend edges 46 run between the longitudinal edges 44 generally parallel tothe transverse axis 110 of the diaper 20. The chassis also comprises afastening system, which may include at least one fastening member 40 andat least one stored landing zone 42.

For unitary absorbent articles, the chassis 22 comprises the mainstructure of the diaper with other features added to form the compositediaper structure. While the topsheet 24, the backsheet 26, and theabsorbent core 28 may be assembled in a variety of well-knownconfigurations, preferred diaper configurations are described generallyin U.S. Pat. No. 5,554,145 entitled “Absorbent Article With MultipleZone Structural Elastic-Like Film Web Extensible Waist Feature” issuedto Roe et al. on Sep. 10, 1996; U.S. Pat. No. 5,569,234 entitled“Disposable Pull-On Pant” issued to Buell et al. on Oct. 29, 1996; andU.S. Patent No. 6,004,306 entitled “Absorbent Article WithMulti-Directional Extensible Side Panels” issued to Robles et al. onDec. 21, 1999.

The topsheet 24 in FIG. 1 may be fully or partially elasticized or maybe foreshortened to provide a void space between the topsheet 24 and theabsorbent core 28. Exemplary structures including elasticized orforeshortened topsheets are described in more detail in U.S. Pat. No.5,037,416 entitled “Disposable Absorbent Article Having ElasticallyExtensible Topsheet” issued to Allen et al. on Aug. 6, 1991; and U.S.Pat. No. 5,269,775 entitled “Trisection Topsheets for DisposableAbsorbent Articles and Disposable Absorbent Articles Having SuchTrisection Topsheets” issued to Freeland et al. on Dec. 14, 1993.

The absorbent core 28 in FIG. 1 generally is disposed between thetopsheet 24 and the backsheet 26. The absorbent core 28 may comprise anyabsorbent material that is generally compressible, conformable,non-irritating to the wearer's skin, and capable of absorbing andretaining liquids such as urine and other certain body exudates. Theabsorbent core 28 may comprise a wide variety of liquid-absorbentmaterials commonly used in disposable diapers and other absorbentarticles such as comminuted wood pulp, which is generally referred to asair felt. Examples of other suitable absorbent materials include crepedcellulose wadding; melt blown polymers, including co-form; chemicallystiffened, modified or cross-linked cellulosic fibers; tissue, includingtissue wraps and tissue laminates; absorbent foams; absorbent sponges;superabsorbent polymers; absorbent gelling materials; or any other knownabsorbent material or combinations of materials. The absorbent core 28may further comprise minor amounts (typically less than 10%) ofnon-liquid absorbent materials, such as adhesives, waxes, oils and thelike.

Exemplary absorbent structures for use as the absorbent assemblies aredescribed in U.S. Pat. No. 4,610,678 (Weisman et al.); U.S. Pat. No.4,834,735 (Alemany et al.); U.S. Pat. 4,888,231 (Angstadt); U.S. Pat.No. 5,260,345 (DesMarais et al.); U.S. Pat. No. 5,387,207 (Dyer et al.);U.S. Pat. No. 5,397,316 (LaVon et al.); and U.S. Pat. No. 5,625,222(DesMarais et al.).

The backsheet 26 may be joined with the topsheet 24. The backsheet 26prevents the exudates absorbed by the absorbent core 28 and containedwithin the article 20 from soiling other external articles that maycontact the diaper 20, such as bed sheets and undergarments. Inpreferred embodiments, the backsheet 26 is substantially impervious toliquids (e.g., urine) and comprises a laminate of a nonwoven and a thinplastic film such as a thermoplastic film having a thickness of about0.012 mm (0.5 mil) to about 0.051 mm (2.0 mils). Suitable backsheetfilms include those manufactured by Tredegar Industries Inc. of TerreHaute, Ind. and sold under the trade names X15306, X10962, and X10964.Other suitable backsheet materials may include breathable materials thatpermit vapours to escape from the diaper 20 while still preventingexudates from passing through the backsheet 26. Exemplary breathablematerials may include materials such as woven webs, nonwoven webs,composite materials such as film-coated nonwoven webs, and microporousfilms such as manufactured by Mitsui Toatsu Co., of Japan under thedesignation ESPOIR NO and by EXXON Chemical Co., of Bay City, Tex.,under the designation EXXAIRE. Suitable breathable composite materialscomprising polymer blends are available from Clopay Corporation,Cincinnati, Ohio under the name HYTREL blend P18-3097. Such breathablecomposite materials are described in greater detail in PCT ApplicationNo. WO 95/16746, published on Jun. 22, 1995 in the name of E. I. DuPont.Other breathable backsheets including nonwoven webs and apertured formedfilms are described in U.S. Pat. No. 5,571,096 issued to Dobrin et al.on Nov. 5, 1996.

The diaper 20 may also include such other features as are known in theart including front and rear ear panels, waist cap features, elasticsand the like to provide better fit, containment and aestheticcharacteristics. Such additional features are well known in the art andare e.g., described in U.S. Pat. No. 3,860,003 and U.S. Pat. No.5,151,092.

In order to keep the diaper 20 in place about the wearer, preferably atleast a portion of the first waist region 36 is attached by thefastening member 42 to at least a portion of the second waist region 38,preferably to form leg opening(s) and an article waist. When fastened,the fastening system carries a tensile load around the article waist.The fastening system is designed to allow an article user to hold oneelement of the fastening system such as the fastening member 42, andconnect the first waist region 36 to the second waist region 38 in atleast two places. This is achieved through manipulation of bondstrengths between the fastening device elements.

Diapers 20 according to the present invention may be provided with are-closable fastening system or may alternatively provided in the formof pant-type diapers.

The fastening system and any component thereof may include any materialsuitable for such a use, including but not limited to plastics, films,foams, nonwoven webs, woven webs, paper, laminates, fiber reinforcedplastics and the like, or combinations thereof. It may be preferablethat the materials making up the fastening device be flexible. Theflexibility is designed to allow the fastening system to conform to theshape of the body and thus, reduces the likelihood that the fasteningsystem will irritate or injure the wearer's skin.

FIG. 2 shows a cross section of FIG. 1 taken along the sectional line2-2 of FIG. 1. Starting from the wearer facing side the diaper comprisesthe topsheet 24, the components of the absorbent core 28, and thebacksheet 26. The absorbent article preferably comprises an acquisitionsystem 50, which comprises an upper acquisition layer 52 facing thetowards the wearer's skin and an lower acquisition 54 layer facing thegarment of the wearer. In one preferred embodiment the upper acquisitionlayer 52 comprises a non-woven whereas the lower acquisition layerpreferably comprises a mixture of chemically stiffened, twisted andcurled fibers, high surface area fibers and thermoplastic bindingfibers. In another preferred embodiment both acquisition layers areprovided from a non-woven material, which is preferably hydrophilic Theacquisition layer preferably may be in direct contact with the storagelayer 60.

The storage layer 60 may be wrapped by a core wrap material. In onepreferred embodiment the core wrap material comprises a top layer 56 anda bottom layer 58. The core wrap material, the top layer 56 or thebottom layer 58 can be provided from a non-woven material. One preferredmaterial is a so called SMS material, comprising a spunbonded, amelt-blown and a further spunbonded layer. Highly preferred arepermanently hydrophilic non-wovens, and in particular nonwovens withdurably hydrophilic coatings. An alternative preferred materialcomprises a SMMS-structure.

The top layer 56 and the bottom layer 58 may be provided from two ormore separate sheets of materials or they may be alternatively providedfrom a unitary sheet of material. Such a unitary sheet of material maybe wrapped around the storage layer 60 e.g., in a C-fold.

Preferred non-woven materials are provided from synthetic fibers, suchas PE, PET and most preferably PP. As the polymers used for nonwovenproduction are inherently hydrophobic, they are preferably coated withhydrophilic coatings.

A preferred way to produce nonwovens with durably hydrophilic coatings,is via applying a hydrophilic monomer and a radical polymerizationinitiator onto the nonwoven, and conducting a polymerization activatedvia UV light resulting in monomer chemically bound to the surface of thenonwoven as described in co-pending U.S. patent application Ser. No.10/674,670.

An alternative preferred way to produce nonwovens with durablyhydrophilic coatings is to coat the nonwoven with hydrophilicnanoparticles as described in co-pending application Ser. No. 10/060,708and WO 02/064877.

Typically, nanoparticles have a largest dimension of below 750 nm.Nanoparticles with sizes ranging form 2 to 750 nm can be economicallyproduced. The advantages of nanoparticles is that many of them can beeasily dispersed in water solution to enable coating application ontothe nonwoven; they typically form transparent coatings, and the coatingsapplied from water solutions are typically sufficiently durable toexposure to water.

Nanoparticles can be organic or inorganic, synthetic or natural.Inorganic nanoparticles generally exist as oxides, silicates,carbonates. Typical examples of suitable nanoparticles are layered clayminerals (e.g., LAPONITE™ from Southern Clay Products, Inc. (USA), andBoehmite alumina (e.g., Disperal P2™ from North American Sasol. Inc.)

A highly preferred nanoparticle coated non-woven is disclosed in theco-pending patent application Ser. No. 10/758,066 entitled “Disposableabsorbent article comprising a durable hydrophilic core wrap” toEkaterina Anatolyevna Ponomarenko and Mattias NMN Schmidt.

Further useful non-wovens are described in U.S. Pat. No. 6,645,569 toCramer et al. and co-pending patent applications Ser. Nos. 10/060,694 toCramer et al., 10/060,708 to Rohrbaugh et al., 10/338,603 to Cramer etal., and 10/338,610 to Cramer et al.

In some cases, the nonwoven surface can be pre-treated with high energytreatment (corona, plasma) prior to application of nanoparticlecoatings. High energy pre-treatment typically temporarily increases thesurface energy of a low surface energy surface (such as PP) and thusenables better wetting of a nonwoven by the nanoparticle dispersion inwater.

Notably, permanently hydrophilic non-wovens are also useful in otherparts of an absorbent article. For example, topsheets and acquisitionlayers comprising permanently hydrophilic non-wovens as described abovehave been found to work well.

The surface tension is a measure of how permanently a certainhydrophilicity level is achieved. The value is to be measured using thetest method described hereinbelow.

The liquid strike through time is a measure of a certain hydrophilicitylevel. The value is to be measured using the test method describedhereinbelow.

In a preferred embodiment of the present invention the absorbent core 28comprises a substrate layer 100, absorbent polymer material 110 and afibrous layer of adhesive 120. The substrate layer 100 is preferablyprovided from a non-woven material, preferred non-wovens are thoseexemplified above for the top layer 56 or the bottom layer 58.

In accordance with the present invention, the absorbent material isimmobilized when wet such that the absorbent core achieves a wetimmobilization of more than 50%, preferably of more than 60%, 70%, 80%or 90% according to the Wet Immobilization Test described herein.

The substrate layer 100 comprises a first surface and a second surface.At least portions of the first surface of the substrate layer 100 are indirect contact with a layer of absorbent polymer material 110. Thislayer of absorbent polymer material 110 is preferably a discontinuouslayer, and comprises a first surface and a second surface. As usedherein, a discontinuous layer is a layer comprising openings. Typicallythese openings have a diameter or largest span of less than 10 mm,preferably less than 5 mm, 3 mm, 2 mm and of more than 0.5 mm, 1 mm or1.5 mm. At least portion of the second surface of the absorbent polymermaterial layer 110 are in contact with at least portions of the firstsurface of the substrate layer material 100. The first surface of theabsorbent polymer material 110 defines a certain height 112 of the layerof absorbent polymer above the first surface of the layer of substratematerial 100. When the absorbent polymer material layer 110 is providedas a discontinuous layer, portions of the first surface of the substratelayer 100 are not covered by absorbent polymer material 110. Theabsorbent core 28 further comprises a thermoplastic composition 120.This thermoplastic composition 120 serves to at least partiallyimmobilize the absorbent polymer material 110.

In one preferred embodiment of the present invention the thermoplasticcomposition 120 can be disposed essentially uniformly within thepolymeric absorbent material 110.

However, in an even more preferred embodiment of the present inventionthe thermoplastic material 120 is provided as a fibrous layer which ispartially in contact with the absorbent polymer material 110 andpartially in contact with the substrate layer 100. FIG. 3 shows such apreferred structure. In this preferred structure the absorbent polymermaterial layer 110 is provided as a discontinuous layer, a layer offibrous thermoplastic material 120 is laid down onto the layer ofabsorbent polymeric material 110, such that the thermoplastic layer 120is in direct contact with the first surface of the layer of absorbentpolymer material 110, but also in direct contact with the first surfaceof the substrate layer 100, where the substrate layer is not covered bythe absorbent polymeric material 110. This imparts an essentiallythree-dimensional structure to the fibrous layer of thermoplasticmaterial 120 which in itself is essentially a two-dimensional structureof relatively small thickness (in z-direction), as compared to theextension in x- and y-direction. In other words, the fibrousthermoplastic material layer 120 undulates between the first surface ofthe absorbent polymer material 110 and the first surface of thesubstrate layer 100.

Thereby, the thermoplastic material 120 provides cavities to hold theabsorbent polymer material 110, and thereby immobilizes this material.In a further aspect, the thermoplastic material 120 bonds to thesubstrate 100 and thus affixes the absorbent polymer material 110 to thesubstrate 100. Highly preferred thermoplastic materials will alsopenetrate into both the absorbent polymer material 110 and the substratelayer 100, thus providing for further immobilization and affixation.

Of course, while the thermoplastic materials disclosed herein provide amuch improved wet immobilisation (i.e., immobilisation of absorbentmaterial when the article is wet or at least partially loaded), thesethermoplastic materials also provide a very good immobilisation ofabsorbent material when the article is dry.

In accordance with the present invention, the absorbent polymer material110 may also be mixed with absorbent fibrous material, such as airfeltmaterial, which can provide a matrix for further immobilization of thesuper-absorbent polymer material. However, preferably a relatively lowamount of fibrous cellulose material is used, preferably less than 40weight %, 20 or 10 weight % of cellulose fibrous material as compared tothe weight of absorbent polymer material 110. Substantially airfelt freecores are preferred. As used herein, the term “absorbent fibrousmaterial” is not meant to refer to any thermoplastic material (120) evenif such thermoplastic material is fiberized and partially absorbent.

An alternative preferred embodiment of the present invention is shown inFIG. 4. The absorbent core shown in FIG. 4 further comprises a coverlayer 130. This cover layer may be provided of the same material as thesubstrate layer 100, or may be provided from a different material.Preferred materials for the cover layer are the non-woven materials,typically the materials described above as useful for the top layer 56and the bottom layer 58. In this embodiment portions of the cover layer130 bond to portions of the substrate layer 100 via the thermoplasticmaterial 120. Thereby, the substrate layer 100 together with the coverlayer 130 provides cavities to immobilize the absorbent polymer material110.

With reference to FIGS. 3 and 4 the areas of direct contact between thethermoplastic material 120 and the substrate material 100 are referredto as areas of junction 140. The shape number and disposition of theareas of junction 140 will influence the immobilization of the absorbentpolymer material 110. The areas of junction can be of squared,rectangular or circular shape. Preferred areas of junction are ofcircular shape. Preferably, they have a diameter of more than 0.5 mm, or1 mm, or 1.5 mm and of less than 10 mm, or 5 mm, or 3 mm, or 2 mm. Ifthe areas of junction 140 are not of circular shape, they preferably areof a size as to fit inside a circle of any of the preferred diametersgiven above.

The areas of junction 140 can be disposed in a regular or irregularpattern. For example, the areas of junction 140 may be disposed alonglines as shown in FIG. 5. These lines may be aligned with thelongitudinal axis of the absorbent core, or alternatively they may havea certain angle in respect to the longitudinal edges of the core. It hasbeen found, that a disposition along lines parallel with thelongitudinal edges of the absorbent core 28 create channels in thelongitudinal direction which lead to a lesser wet immobilization.Preferably, therefore the areas of junction 140 are arranged along lineswhich form an angle of 20 degree, 30 degree, 40 degree, or 45 degreewith the longitudinal edges of the absorbent core 28. Another preferredpattern for the areas of junction 140 is a pattern comprising polygons,for example pentagons and hexagons or a combination of pentagons andhexagons. Also preferred are irregular patterns of areas of junction140, which also have been found to give a good wet immobilization.

Two fundamentally different patterns of areas of junctions 140 can bechosen in accordance with the present invention. In one embodiment theareas of junctions are discrete. They are positioned within the areas ofabsorbent material, like islands in a sea. The areas of absorbentmaterials are then referred to as connected areas. In an alternativeembodiment, the areas of junctions can be connected. Then, the absorbentmaterial can be deposited in a discrete pattern, or in other words theabsorbent material represents islands in a sea of thermoplastic material120. Hence, a discontinuous layer of absorbent polymer material 110 maycomprise connected areas of absorbent polymer material 110 or maycomprise discrete areas of absorbent polymer material 110.

In a further aspect of the present invention, it has been found thatabsorbent cores providing for a good wet immobilization can be formed bycombining two layers as shown in FIG. 3 and as described in the contextthereof. Such an embodiment is shown in FIG. 6. The absorbent corematerial shown in FIG. 6 comprises two substrate layers 100, two layersof absorbent polymer material 110 and two layers of fibrousthermoplastic materials 120. When two discontinuous layers of anabsorbent polymer material 110 are used, they would be typicallyarranged in such a way that the absorbent polymer material of the onelayer faces the areas of junction 140 of the other layer. In analternative preferred embodiment, however, the areas of junction 140 areoffset and do not face each other. Hence preferably, when two storagelayers are joined, this is done such that the first surface of thesubstrate layer 100 of the first storage layer 60 faces the firstsurface of the substrate layer 100 of the second storage layer 60.

The present invention, and specifically the preferred embodimentdescribed with reference to FIGS. 3, 4 and 6 can be used to provide thestorage layer 60 of an absorbent core. However, they can also be used toprovide the full absorbent core 28. In that case, no further materialswrapping the core, such as the top layer 56 and the bottom layer 58 arebeing used. With reference to the embodiment of FIG. 3 the substratelayer 100 may provide the function of the bottom layer 58 and the layerof fibrous thermoplastic material 120 may provide the function of thetop layer 56. With reference to FIG. 4 the cover layer 130 may providethe function of the top layer 56 and the substrate layer 100 may providethe function of the bottom layer 58. With reference to FIG. 6, the twosubstrate layers 100 used may provide the functions of the top layer 56and the bottom layer 58, respectively.

According to the present invention the thermoplastic layer 120 cancomprise any thermoplastic composition, preferred are adhesivethermoplastic compositions, also referred to as hot melt adhesives. Avariety of thermoplastic compositions are suitable to immobilizeabsorbent material.

Some initially thermoplastic materials may later lose theirthermoplasticity due to a curing step, e.g., initiated via heat, UVradiation, electron beam exposure or moisture or other means of curing,leading to the irreversible formation of a crosslinked network ofcovalent bonds. Those materials having lost their initial thermoplasticbehaviour are herein also understood as thermoplastic materials 120.

Without wishing to be bound by theory it has been found that thosethermoplastic compositions are most useful for immobilizing theabsorbent polymer material 110, which combine good cohesion and goodadhesion behaviour. Good adhesion is critical to ensure that thethermoplastic layer 120 maintains good contact with the absorbentpolymer material 110 and in particular with the substrate. Good adhesionis a challenge, namely when a non-woven substrate is used. Good cohesionensures that the adhesive does not break, in particular in response toexternal forces, and namely in response to strain. The adhesive issubject to external forces when the absorbent product has acquiredliquid, which is then stored in the absorbent polymer material 110 whichin response swells. A preferred adhesive will allow for such swelling,without breaking and without imparting too many compressive forces,which would restrain the absorbent polymer material 110 from swelling.Importantly, in accordance with the present invention the adhesiveshould not break, which would deteriorate the wet immobilization.Preferred thermoplastic compositions meeting these requirements have thefollowing features:

The thermoplastic composition may comprise, in its entirety, a singlethermoplastic polymer or a blend of thermoplastic polymers, having asoftening point, as determined by the ASTM Method D-36-95 “Ring andBall”, in the range between 50° C. and 300° C., or alternatively thethermoplastic composition may be a hot melt adhesive comprising at leastone thermoplastic polymer in combination with other thermoplasticdiluents such as tackifying resins, plasticizers and additives such asantioxidants.

The thermoplastic polymer has typically a molecular weight (Mw) of morethan 10,000 and a glass transition temperature (Tg) usually below roomtemperature. Typical concentrations of the polymer in a hot melt are inthe range of 20-40% by weight. A wide variety of thermoplastic polymersare suitable for use in the present invention. Such thermoplasticpolymers are preferably water insensitive. Exemplary polymers are(styrenic) block copolymers including A-B-A triblock structures, A-Bdiblock structures and (A-B)n radial block copolymer structures whereinthe A blocks are non-elastomeric polymer blocks, typically comprisingpolystyrene, and the B blocks are unsaturated conjugated diene or(partly) hydrogenated versions of such. The B block is typicallyisoprene, butadiene, ethylene/butylene (hydrogenated butadiene),ethylene/propylene (hydrogenated isoprene), and mixtures thereof.

Other suitable thermoplastic polymers that may be employed aremetallocene polyolefins, which are ethylene polymers prepared usingsingle-site or metallocene catalysts. Therein, at least one comonomercan be polymerized with ethylene to make a copolymer, terpolymer orhigher order polymer. Also applicable are amorphous polyolefins oramorphous polyalphaolefins (APAO) which are homopolymers, copolymers orterpolymers of C2 to C8 alphaolefins.

The resin has typically a Mw below 5,000 and a Tg usually above roomtemperature, typical concentrations of the resin in a hot melt are inthe range of 30-60%. The plasticizer has a low Mw of typically less than1,000 and a Tg below room temperature, a typical concentration is 0-15%.

Preferably the adhesive is present in the forms of fibres throughout thecore, i.e., the adhesive is fiberized. Preferably, the fibres will havean average thickness of 1-50 micrometer and an average length of 5 mm to50 cm.

To improve the adhesion of the thermoplastic material 120 to thesubstrate layer 100 or to any other layer, in particular any othernon-woven layer, such layers may be pre-treated with an auxiliaryadhesive.

Preferably, the adhesive will meet at least one, and more preferablyseveral or all of the following parameters:

A preferred adhesive will have a storage modulus G′ measured at 20° C.of at least 30,000 Pa and less than 300,000 Pa preferably less than200,000 Pa, more preferably less than 100,000 Pa. The storage modulus G′at 20° C. is a measure for the permanent “tackiness” or permanentadhesion of the thermoplastic material used. Good adhesion will ensure agood and permanent contact between the thermoplastic material and forexample the substrate layer 100. In a further aspect, the storagemodulus G′ measured at 60° C. should be less than 300,000 Pa and morethan 18,000 Pa, preferably more than 24,000 Pa, most preferably morethan 30,000. The storage modulus measured at 60° C. is a measure for theform stability of the thermoplastic material at elevated ambienttemperatures. This value is particularly important if the absorbentproduct is used in a hot climate where the thermoplastic compositionwould lose its integrity if the storage modulus G′ at 60° C. is notsufficiently high.

G′ is typically measured using a rheometer as schematically shown inFIG. 8 for the purpose of general illustration only. The rheometer 400is capable of applying a shear stress to the adhesive and measuring theresulting strain (shear deformation) response at constant temperature.The adhesive is placed between a Peltier-element acting as lower, fixedplate 410 and an upper plate 420 with a radius R of e.g., 10 mm, whichis connected to the drive shaft of a motor to generate the shear stress.The gap between both plates has a height H of e.g., 1500 micron. ThePeltier-element enables to control the temperature of the material(±0.5° C.).

In a further aspect, the loss angle tan Delta of the adhesive at 60° C.should be below the value of 1, preferably below the value of 0.5. Theloss angle tan Delta at 60° C. is correlated with the liquid characterof an adhesive at elevated ambient temperatures. The lower tan Delta,the more an adhesive behaves like a solid rather than a liquid, i.e.,the lower its tendency to flow or to migrate and the lower the tendencyof an adhesive superstructure as described herein to deteriorate or evento collapse over time. This value is hence particularly important if theabsorbent article is used in a hot climate.

In a further aspect, the preferred adhesive should have a glasstransition temperature T_(g) of less than 25° C., preferably less than22° C., more preferably less than 18° C., and most preferably less than15° C. A low glass transition temperature T_(g) is beneficial for goodadhesion. In a further aspect a low glass transition temperature Tgensures that the adhesive thermoplastic material does not become toobrittle.

In yet a further aspect, a preferred adhesive will have a sufficientlyhigh cross-over temperature T_(x). A sufficiently high cross-overtemperature T_(x) has been found beneficial for high temperaturestability of the thermoplastic layer and hence it ensures goodperformance of the absorbent product and in particular good wetimmobilization even under conditions of hot climates and hightemperatures. Therefore, T_(x) should preferably be above 80° C., morepreferably above 85° C., and most preferably above 90° C.

A highly preferred adhesive useful as a thermoplastic material 120 asdescribed herein will meet most or all of the above parameters. Specificcare must be taken to ensure that the adhesive provides good cohesionand good adhesion at the same time.

The process for producing preferred absorbent cores 28 in accordancewith the present invention comprises the following steps:

The absorbent core 28 is laid down onto a laydown drum, which presentsan uneven surface. In a first process step the substrate layer 100 islaid on to the uneven surface. Due to gravity, or preferably by using avacuum means, the substrate layer material will follow the contours ofthe uneven surface and thereby the substrate layer material will assumea mountain and valley shape. Onto this substrate layer 100 absorbentpolymeric material is disposed by means known in the art. The absorbentpolymer material will accumulate in the valleys presented by thesubstrate layer 100. In a further process step a hot melt adhesive isplaced onto the absorbent polymer material.

While any adhesive application means known in the art can be used toplace the hot melt adhesive on to the absorbent polymer material, thehot melt adhesive is preferably applied by a nozzle system. Preferably,a nozzle system is utilised, which can provide a relatively thin butwide curtain of adhesive. This curtain of adhesive is than placed ontothe substrate layer 100 and the absorbent polymer material. As themountain tops of the substrate layer 100 are less covered by absorbentpolymer material the adhesive will make contact with these areas of thesubstrate layer.

In an optional further process step a cover layer 130 is placed upon thesubstrate layer 100, the absorbent polymer material and the hot meltadhesive layer. The cover layer 130 will be in adhesive contact with thesubstrate layer 100 in the areas of junction 140. In these areas ofjunction 140 the adhesive is in direct contact with the substrate layer100. The cover layer 130 will typically not be in adhesive contact withthe substrate layer 100 where the valleys of the substrate layer 100 arefilled with absorbent polymer material.

Alternatively the cover layer 130 can be laid down onto a drum with anuneven surface and the substrate layer 100 can be added in a consecutiveprocess step. The embodiment shown in FIG. 4 could be produced by such aprocess.

In one alternative embodiment, the cover layer 130 and the substratelayer 100 are provided from a unitary sheet of material. The placing ofthe cover layer 130 onto the substrate layer 100 will then involve thefolding of the unitary piece of material.

Hence, the uneven surface of the lay-down system, which preferably is alay-down drum, typically determines the distribution of absorbentpolymeric material throughout the storage layer 60 and likewisedetermines the pattern of areas of junction 140. Alternatively, thedistribution of absorbent polymeric material may be influenced by vacuummeans.

Preferably the distribution of absorbent polymeric material is profiledand most preferably profiled in the longitudinal direction. Hence, alongthe longitudinal axis of the absorbent core, which is normallycoincident with the longitudinal axis of the absorbent article, forexample of the diaper, the basis weight of the absorbent polymermaterial will change. Preferably the basis weight of absorbent polymermaterial in at least one freely selected first square measuring 1 cm×1cm is at least 10%, or 20%, or 30%, 40% or 50% higher than the basisweight of absorbent polymer material in at least one freely selectedsecond square measuring 1 cm×1 cm. Preferably the criterion is met ifthe first and the second square are centred about the longitudinal axis.

Optionally, the absorbent core can also comprise an absorbent fibrousmaterial, for example cellulose fibres. This fibrous material can bepre-mixed with the absorbent polymeric material and be laid down in oneprocess step or it can alternatively be laid-down in separate processsteps.

It has been found beneficial to use a particulate absorbent polymermaterial for absorbent cores made in the present invention. Withoutwishing to be bound by theory it is believed that such material, even inthe swollen state, i.e., when liquid has been absorbed, does notsubstantially obstruct the liquid flow throughout the material,especially when the permeability as expressed by the saline flowconductivity of the absorbent polymer material is greater than 10, 20,30 or 40 SFC- units, where 1 SFC unit is 1×10⁻⁷ (cm³×s) / g. Saline flowconductivity is a parameter well recognised in the art and is to bemeasured in accordance with the test disclosed in U.S. Pat. No.5,599,335.

As disclosed in U.S. Pat. No. 5,599,335, an important characteristic ofthe hydrogel-forming absorbent polymers useful in the present inventionis their permeability or flow conductivity when swollen with body fluidsso as to form a hydrogel zone or layer. This permeability or flowconductivity is defined herein in terms of the Saline Flow Conductivity(SFC) value of the hydrogel-forming absorbent polymer. SFC measures theability of the formed hydrogel zone or layer to transport or distributebody fluids under usage pressures. It is believed that when ahydrogel-forming absorbent polymer is present at high concentrations inan absorbent member and then swells to form a hydrogel under usagepressures, the boundaries of the hydrogel come into contact, andinterstitial voids in this high-concentration region become generallybounded by hydrogel. When this occurs, it is believed the permeabilityor flow conductivity properties of this region are generally reflectiveof the permeability or flow conductivity properties of a hydrogel zoneor layer formed from the hydrogel-forming absorbent polymer alone. It isfurther believed that increasing the permeability of these swollenhigh-concentration regions to levels that approach or even exceedconventional acquisition/distribution materials, such as wood-pulpfluff, can provide superior fluid handling properties for the absorbentmember and absorbent core, thus decreasing incidents of leakage,especially at high fluid loadings. (Higher SFC values also arereflective of the ability of the formed hydrogel to acquire body fluidsunder normal usage conditions.)

The SFC value of the hydrogel-forming absorbent polymers useful in thepresent invention is at least about 30×10⁻⁷ cm³ sec/g, preferably atleast about 50×10⁻⁷ cm³ sec/g, and most preferably at least about100×10⁻⁷ cm³ sec/g. Typically, these SFC values are in the range of fromabout 30 to about 1000×10⁻⁷ cm³ sec/g, more typically from about 50 toabout 500×10⁻⁷ cm³ sec/g, and most typically from about 100 to about350×10⁻⁷ cm³ sec/g. A method for determining the SFC value of thesehydrogel-forming absorbent polymers is as follows:

The Saline Flow Conductivity (SFC) test determines the Saline FlowConductivity (SFC) of the gel layer formed from hydrogel-formingabsorbent polymer that is swollen in Jayco synthetic urine under aconfining pressure. The objective of this test is to assess the abilityof the hydrogel layer formed from a hydrogel-forming absorbent polymerto acquire and distribute body fluids when the polymer is present athigh concentrations in an absorbent member and exposed to usagemechanical pressures. Darcy's law and steady-state flow methods are usedfor determining saline flow conductivity. (See, for example,“Absorbency,” ed. by P. K. Chatterjee, Elsevier, 1985, Pages 42-43 and“Chemical Engineering Vol. II, Third Edition, J. M. Coulson and J. F.Richardson, Pergamon Press, 1978, Pages 125-127.)

The hydrogel layer used for SFC measurements is formed by swelling ahydrogel-forming absorbent polymer in Jayco synthetic urine for a timeperiod of 60 minutes. The hydrogel layer is formed and its flowconductivity measured under a mechanical confining pressure of 0.3 psi(about 2 kPa). Flow conductivity is measured using a 0.118M NaClsolution. For a hydrogel-forming absorbent polymer whose uptake of Jaycosynthetic urine versus time has substantially leveled off, thisconcentration of NaCl has been found to maintain the thickness of thehydrogel layer substantially constant during the measurement. For somehydrogel-forming absorbent polymers, small changes in hydrogel-layerthickness can occur as a result of polymer swelling, polymer deswelling,and/or changes in hydrogel-layer porosity. A constant hydrostaticpressure of 4920 dyne/cm² (5 cm of 0.118M NaCl) is used for themeasurement.

Flow rate is determined by measuring the quantity of solution flowingthrough the hydrogel layer as a function of time. Flow rate can varyover the duration of the measurement. Reasons for flow-rate variationinclude changes in the thickness of the hydrogel layer and changes inthe viscosity of interstitial fluid, as the fluid initially present ininterstitial voids (which, for example, can contain dissolvedextractable polymer) is replaced with NaCl solution. If flow rate istime dependent, then the initial flow rate, typically obtained byextrapolating the measured flow rates to zero time, is used to calculateflow conductivity. The saline flow conductivity is calculated from theinitial flow rate, dimensions of the hydrogel layer, and hydrostaticpressure. For systems where the flow rate is substantially constant, ahydrogel-layer permeability coefficient can be calculated from thesaline flow conductivity and the viscosity of the NaCl solution.

A suitable apparatus 610 for this test is shown in FIG. 8. Thisapparatus includes a constant hydrostatic head reservoir indicatedgenerally as 612 that sits on a laboratory jack indicated generally as614. Reservoir 612 has lid 616 with a stoppered vent indicated by 618 sothat additional fluid can be added to reservoir 612. An open-ended tube620 is inserted through lid 616 to allow air to enter reservoir 612 forthe purpose of delivering fluid at a constant hydrostatic pressure. Thebottom end of tube 620 is positioned so as to maintain fluid in cylinder634 at a height of 5.0 cm above the bottom of the hydrogel layer.

Reservoir 612 is provided with a generally L-shaped delivery tube 622having an inlet 622 a that is below the surface of the fluid in thereservoir. The delivery of fluid by tube 622 is controlled by stopcock626. Tube 622 delivers fluid from reservoir 612 to a piston/cylinderassembly generally indicated as 628. Beneath assembly 628 is a supportscreen (not shown) and a collection reservoir 630 that sits on alaboratory balance 632.

Assembly 628 basically consists of a cylinder 634, a piston generallyindicated as 636 and a cover 637 provided with holes for piston 636 anddelivery tube 622. The outlet 622 b of tube 622 is positioned below thebottom end of tube 620 and thus will also be below the surface of thefluid (not shown) in cylinder 634.

As to achieve a sufficient absorbent capacity in a preferred absorbentarticle according to the present invention and especially if theabsorbent article is a diaper or an adult incontinence product,superabsorbent polymer material will be present with an average basisweight of more than 50, 100, 200, 300, 400, 500, 600, 700, 800 or 900g/m².

Preferred articles according to the present invention achieve arelatively narrow crotch width, which increases the wearing comfort. Apreferred article according to the present invention achieves a crotchwidth of less than 100 mm, 90 mm, 80 mm, 70 mm, 60 mm or even less than50 mm. Hence, preferably an absorbent core according to the presentinvention has a crotch width as measured along a transversal line whichis positioned at equal distance to the front edge and the rear edge ofthe core which is of less than 100 mm, 90 mm, 80 mm, 70 mm, 60 mm oreven less than 50 mm. It has been found that for most absorbent articlesthe liquid discharge occurs predominately in the front half. The fronthalf of the absorbent core should therefore comprise most of theabsorbent capacity of the core. Preferably the front half of saidabsorbent core comprises more than 60% of the absorbent capacity, morepreferably more than 65%, 70%, 75%, 80%, 85%, or 90%.

All patents and patent applications (including any patents which issuethereon) assigned to the Procter & Gamble Company referred to herein arehereby incorporated by reference to the extent that it is consistentherewith.

Wet Immobilization Test

Equipment:

Test solution: 0.90% saline solution at 37° C.

Balance

Diaper Shaker

Bath for keeping test solution at 35-37° C.

Graduated fluid beaker, at least 2 ml steps

Stop watch

Thermometer

Tray (300) of about 10×120×220 mm

Diaper Shaker

A test set up for carrying out the wet immobilisation test may comprisea so called “diaper shaker” as described herein and as shown in FIG. 7.The shaker comprises a base plate 210, which should be of sufficientweight to allow stable shaking conditions. Mounted onto the base plateis are two legs 220 a and 220 b, which are height adjustable to testabsorbent cores or absorbent products of different lengths. The legs 220support a plate 230. Mounted onto this plate using rubber supports 240is the clamp mount table 250. The shaking movement between the clampmount table 250 and the plate 230 is caused by a motor, preferably anelectric motor 260. The clamp mount table 250 is rigidly connected to aclamp 270, the size of which is chosen in correspondence to theabsorbent cores or absorbent products to be evaluated.

The base plate 210 may also be used as a support for the tray 300, inwhich the absorbent core or absorbent products is pre-wetted prior tothe testing operation, as described below.

Sample Preparation:

Provide ten absorbent articles or absorbent core samples. Remove alllayers that do not directly wrap the absorbent polymer material (e.g.,topsheet and backsheet and acquisition layers not comprising absorbentpolymer material) from absorbent article sample. Cut a core sample of200 mm length using two parallel cutting lines of transversalorientation. If the core length exceeds 200 mm any two parallel cuttinglines as defined above can be chosen.

Measure dry laminate weight.

Put the laminate into the tray.

Pour test solution onto the centre of the core sample. Amount of testsolution should be 50% of the laminate design capacity. The designcapacity to the total available capacity of the absorbent cores to betested, and herein is to be understood as laminate CRC capacity of thecut out core sample piece as defined below.

Execute test as described below after 5 min dwell time.

Test Execution:

Measure the wet laminate weight (m1) before the shaking test.

Fix the laminate with clamps such that not less than 180 mm of laminateextends below the clamp, and is therefore not restricted from freemotion during shaking. The clamps need to close over the whole AGMwidth.

The lower free moving laminate end should have a distance to the AGMcollecting tray of 4 cm.

Shaking frequency: 16.8 Hz.

Amplitude in vertical direction: 4 mm, in horizontal direction 1 mm.

Shaking time 2×80 s.

After shaking fix the previous free moving end to the clamp.

Open free moving end, if it was sealed by the pressure of the clamps.

Shake again using the same settings.

Measure remaining laminate weight (m2) after shaking

Result Reporting:

Record dry laminate weight to the nearest tenth gram (e.g.,: 10.0 g)

Record the weight before (m1) and after (m2) shaking, both to thenearest tenth gram (e.g., m1=130.4 g, m2=100.4 g)

Record the average weight loss to the nearest tenth gram (e.g.,: 30.0 g)

Calculate the average weight loss in percent, (m₁−m₂)/m₁)}*100, to thenearest full unit (e.g.,: 23%).

Report the single test wet immobilisation value which is the differencebetween the average weight loss percent and 100% (e.g., 77% wetimmobilisation).

The Wet Immobilisation Value, herein also referred to as wetimmobilisation, is the average value based on ten single test wetimmobilisation values. A high Wet Immobilisation Value is representativeof good wet immobilisation and low particle loss.

Laminate CRC Capacity

Laminate CRC capacity (C_(LAM)) is calculated as:C_(LAM)=m_(AGM).CRC_(AGM)m_(AGM) denotes the mass of AGM in the Laminate. CRC_(AGM) denotes theCRC capacity of the AGM in the laminate.

The mass of AGM inside the laminate (m_(AGM)) may be measured by anyuseful method know to the man skilled in the art e.g., titration may beused.

AGM CRC (CRC_(AGM)) is measured by removing some AGM from the laminateand then applying the Centrifuge Retention Capacity (CRC) test below:

Centrifuge Retention Capacity (CRC)

For most hydrogel-forming absorbent polymers, gel volume as ameasurement of absorbent capacity is determined by the method describedin U.S. Reissue Pat. No. 32,649 (Brandt et al), reissued Apr. 19, 1988but using 0.9% saline solution instead of synthetic urine. The gelvolume as well as the CRC capacity is calculated on a dry-weight basis.This method is to be used for all hydrogel-forming absorbent polymerswhich do not absorb Blue Dextran.

The method for measuring gel volume to be used for SAPs that absorb BlueDextran (see gel volume method in Re 32,649) to the surfaces of theformed hydrogel (e.g., polymers prepared from cationic monomers), is asfollows: For these hydrogel-forming polymers, the Absorptive Capacitytest is used, but the dry weight of the hydrogel-forming polymer is usedin the calculation instead of the as-is weight. See e.g., U.S. Pat. No.5,124,188 (Roe et al), issued Jun. 23, 1992 at Columns 27-28 fordescription of the Absorptive Capacity test.

For the evaluation of the centrifuge retention capacity it has beenfound that the so-called tea-bag-evaluation or measurement (hereinafterCRC measurement) is most appropriate to reflect the maintenance ofcapillary pressure at situations approaching saturation of the absorbentcapability of a SAP material. For the test standard laboratoryconditions (21-23° C., 50% relative humidity) are used. Sample SAPmaterial is kept dry in a tightly closing flask or other container,which is only opened upon start of the evaluation. Other material usedin the evaluation (tissues, equipment etc.) is conditioned for 24 hoursprior to measurements at the above laboratory conditions.

For the CRC measurement 0.2 +/−0.0050 g of SAP particles are put into atea bag (the bag needs to be freely liquid pervious and must retain theparticles, i.e., the tea bag pores need to be not larger than thesmallest particles. The tea bag should have a size of 60 mm×85 mm and issealed by welding after filling. The tea bag is then immersed for 30minutes in a 0.9% saline solution such that there is at least 0.83 l ofsolution per gram of SAP; preferably there is a substantial excess ofthis ratio. After the 30 minute immersion the tea bag is centrifuged at250 g for 3 minutes to remove excess saline solution. The bag is weightto the nearest 0.01 g and the absorbed liquid is calculated. The resultis reported by using the amount of dry SAP, which was put into the teabag, as grams absorbed per gram of SAP particles.

The dimensions and values disclosed herein are not to be understood asbeing strictly limited to the exact numerical values recited. Instead,unless otherwise specified, each such dimension is intended to mean boththe recited value and a functionally equivalent range surrounding thatvalue. For example, a dimension disclosed as “40 mm” is intended to mean“about 40 mm”.

All documents cited in the Detailed Description of the Invention are, inrelevant part, incorporated herein by reference; the citation of anydocument is not to be construed as an admission that it is prior artwith respect to the present invention.

While particular embodiments of the present invention have beenillustrated and described, it would be obvious to those skilled in theart that various other changes and modifications can be made withoutdeparting from the spirit and scope of the invention. It is thereforeintended to cover the appended claims all such changed and modificationthat are within the scope of this invention.

1. An absorbent article comprising: a chassis comprising a topsheet, abacksheet and an absorbent core located between said topsheet and saidbacksheet, wherein said absorbent core comprises: a. a first layercomprising: i. a first substrate material having a first surface and asecond surface, ii. a first absorbent polymer material layer having afirst surface and a second surface, and iii. a first thermoplasticcomposition; wherein at least portions of said second surface of saidfirst absorbent polymer material layer are in contact with at leastportions of said first surface of said first substrate material; whereinat least portions of said first thermoplastic composition are in contactwith at least portions of said first surface of said first absorbentpolymer material layer; and b. a second layer comprising: i. a secondsubstrate material having a first surface and a second surface, ii. asecond absorbent polymer material layer having a first surface and asecond surface, and iii. a second thermoplastic composition; wherein atleast portions of said second surface of said second absorbent polymermaterial layer are in contact with at least portions of said firstsurface of said second substrate material; wherein at least portions ofsaid second thermoplastic composition are in contact with at leastportions of said first surface of said second absorbent polymer materiallayer; wherein said first layer and said second layer are combinedtogether such that said first thermoplastic composition and said secondthermoplastic composition are in direct contact with each other.
 2. Theabsorbent article of claim 1, wherein the absorbent polymer material ofsaid first absorbent polymer material layer and said second absorbentpolymer material layer has a Saline Flow Conductivity of at least about20×10⁻⁷ (cm³×sec)/gram.
 3. The absorbent article of claim 1, wherein theabsorbent polymer material of said first absorbent polymer materiallayer and said second absorbent polymer material layer has a Saline FlowConductivity of at least about 40×10⁻⁷ (cm³×sec)/gram.
 4. The absorbentarticle of claim 1, wherein said absorbent core has less than about 10%of cellulose fibrous material as compared to the weight of the absorbentpolymer material of said first absorbent polymer material layer and saidsecond absorbent polymer material layer.
 5. The absorbent article ofclaim 1, wherein the absorbent polymer material of said first absorbentpolymer material layer and said second absorbent polymer material layeris immobilized when wet such that said absorbent core achieves a wetimmobilization of more than about 50% according to the WetImmobilization Test.
 6. The absorbent article of claim 1, wherein theaverage basis weight of the absorber polymer material of said firstabsorbent polymer material layer and said second absorbent polymermaterial layer is at least about 100 g/m².
 7. The absorbent article ofclaim 1, wherein said first absorbent polymer material layer and saidsecond absorbent polymer material layer are each discontinuous layers.8. The absorbent article of claim 7, wherein said discontinuous layerscomprise openings having a diameter of less than about 10 mm.
 9. Theabsorbent article of claim 7, wherein said discontinuous layers compriseopenings having a diameter of less than about 3 mm.
 10. The absorbentarticle of claim 7, wherein said discontinuous layers comprise openingshaving a diameter of less than about 2 mm.
 11. The absorbent article ofclaim 7, wherein said first thermoplastic composition and said secondthermoplastic composition each provide cavities to hold the absorbentpolymer material of said first absorbent polymer material layer and saidsecond absorbent polymer material layer, respectively.
 12. The absorbentarticle of claim 11, wherein said discontinuous layers are arranged suchthat said cavities comprising said absorbent polymer material of saidfirst absorbent polymer material layer of said first layer are offsetfrom said cavities comprising said absorbent polymer material of saidsecond absorbent polymer material layer of said second layer.
 13. Theabsorbent article of claim 1, wherein said first thermoplasticcomposition and said second thermoplastic composition are a fibrous hotmelt adhesive.
 14. The absorbent article of claim 1, wherein said firstthermoplastic composition and said second thermoplastic compositioncomprise an adhesive having a storage modulus G′ measured at 20° C. ofat least about 30,000 Pa.
 15. The absorbent article of claim 1, whereinsaid first thermoplastic composition and said second thermoplasticcomposition comprise an adhesive having a storage modulus G′ measured at20° C. of less than about 300,000 Pa.
 16. The absorbent article of claim1, wherein said first thermoplastic composition and said secondthermoplastic composition comprise an adhesive having a storage modulusG′ measured at 60° C. of at least about 18,000 Pa.
 17. The absorbentarticle of claim 1, wherein said first thermoplastic composition andsaid second thermoplastic composition comprise an adhesive having astorage modulus G′ measured at 60° C. of less than about 300,000 Pa. 18.The absorbent article of claim 1, wherein said absorbent article is adiaper further comprising a re-closable fastening system joined to saidchassis for securing said diaper to a wearer.
 19. The absorbent articleof claim 1, wherein said absorbent article is a pant-type diaper furthercomprising at least two side panels joined to said chassis and to eachother to form a pant.
 20. An absorbent core comprising: a. a first layercomprising: i. a first substrate material having a first surface and asecond surface, ii. a first absorbent polymer material layer having afirst surface and a second surface, and iii. a first thermoplasticcomposition; wherein at least portions of said second surface of saidfirst absorbent polymer material layer are in contact with at leastportions of said first surface of said first substrate material; whereinat least portions of said first thermoplastic composition are in contactwith at least portions of said first surface of said first absorbentpolymer material layer; and b. a second layer comprising: i. a secondsubstrate material having a first surface and a second surface, ii. asecond absorbent polymer material layer having a first surface and asecond surface, and iii. a second thermoplastic composition; wherein atleast portions of said second surface of said second absorbent polymermaterial layer are in contact with at least portions of said firstsurface of said second substrate material; wherein at least portions ofsaid second thermoplastic composition are in contact with at leastportions of said first surface of said second absorbent polymer materiallayer; wherein said first layer and said second layer are combinedtogether such that said first thermoplastic composition and said secondthermoplastic composition are in direct contact with each other.